A tilelive wrapper that transparently adds streaming functionality to providers.
This module adds createReadStream and createWriteStream methods to
providers that support getTile and putTile respectively. Default
functionality uses a tilelive.Scheme to generate a set of getTile requests,
outputting a stream of streams containing tile data.
var tilelive = require("tilelive-streaming")(require("@mapbox/tilelive"), {
concurrency: 8
});
require("@mapbox/mbtiles").registerProtocols(tilelive);
tilelive.load("mbtiles://./in.mbtiles", function(err, source) {
return tilelive.load("mbtiles://./out.mbtiles", function(err, sink) {
source.createReadStream().pipe(sink.createWriteStream());
});
});createReadStream passes its options into a tilelive.Scheme subclass
(specified by sourceConfig.scheme, defaulting to scanline), so the documentation
for that takes precedence. In practice, minzoom, maxzoom, and bounds are
likely candidates, as they can be used for filtering.
createWriteStream accepts an info option containing TileJSON. Its values
will overwrite any info provided by the source (when appropriate).
Writable streams will emit tile events (containing z, x, y, headers,
and data properties) when data for a given tile has been fully received.
Readable streams will emit info events once it has been loaded (usually
before tile data begins being sent).
lib/ contains specific implementations for providers that do not (yet)
support streaming natively and where the default behavior can be improved upon.
mbtiles is a good example of this,
as the actual list of tiles present can be determined directly from the source
(rather than scanning a bounding box and zoom range for possible candidates).
mbtiles' createReadStream accepts a batchSize argument that allows the
number of tiles read from the underlying SQLite3 database at a time to be
specified.